The present invention relates to a frequency converter utilized as a receiver for television satellite broadcasting.
A frequency converter for the above-mentioned use is generally constituted as shown in FIG. 5, wherein numeral 1 is a high-frequency input terminal connected to an antenna, and the like, numeral 2 is a low-noise amplifier to amplify an input signal from the input terminal 1 up to a prescribed level, numeral 3 is a band pass filter (referred as BPF hereinafter) to pass only a signal within a prescribed frequency band, numeral 4 is a local oscillator and numeral 5 is a mixer to mix a frequency signal from the BPF 3 and a frequency signal from the local oscillator 4 so as to make a diferential frequency signal (beat frequency signal) between them. Numeral 6 is an output terminal to supply an intermediate frequency signal from the mixer 5 to an amplifier of the next stage.
Hitherto, in the case of utilizing a frequency band of 4 GHz, the above-mentioned frequency converter has been fabricated as a plurality of circuit boards one of which corresponds to each of the above circuits (blocks), wherein the boards are isolated from one another by a metalic shield box, or the like, and connected to each other. The reason why the circuits are not fabricated on a common (single) board might be considered as follows: In a 4 GHz frequency band, the dimension of a board becomes larger than that in the case of 12 GHz. In assembling the common boards compactly, there have been problems in interference between the circuits. This also results from the fact that the frequency converter is a device wherein the latest microwave technology is widely employed, that is to say, a high stabilized oscillator, a super low-noise amplifier, and the like are included in the frequency converter. However, when the circuit is fabricated individually or separately, the whole construction of the circuit becomes complicated, whereby it is difficult to realize a satisfactory mass productivity, a good yield of production or a good reliability of the fabricated converter.
It is an object of the invention to provide a circuit for frequency conversion wherein each of the circuits is built-in onto a single board on which a shielding means between the circuits is not provided, thereby a mass productivity, yield of production and reliability of the fabricated frequency converter are greatly improved.
This and other objects of the invention will become apparent from the description hereinafter.